As is known, a premix burner flame is characterized by lower temperature (1500° C. as compared with 2000° C. typical of a diffusion flame) and therefore lower nitric oxide emissions.
In known solutions, the central secondary burner comprises a nozzle extending along the axis of the gas combustor, and which supplies an air stream and two separate fuel gas streams: a first fuel gas stream is fed to the combustion chamber, where it mixes with the air to produce a diffusion flame when igniting and starting up the gas turbine; and, once the system exceeds a given power or load after start-up, the premix burner is activated, the central secondary burner feeds a second fuel gas stream into the combustion chamber to keep a pilot flame, for stabilizing the premix burner flame, alight, and the first fuel gas stream is cut off.
Known solutions as described above therefore call for conduits and valve assemblies by which to feed and control two separate fuel gas streams through the central secondary burner.
In the known gas combustor described above, forming and/or connecting the conduits upstream from the central secondary burner nozzle involve/s a good deal of time and money, and relatively complex systems are required to control the valve assemblies.